Safety capacitor housing model

What is a safety capacitor?

Safety capacitors are also called EMI / RFI suppression capacitors, AC line filter safety capacitors, or X- and Y-rated capacitors. X and Y capacitors not only keep radio frequency noise generated by the device local to that device, but also protect the device from mains noise and high voltage surges.

What is a Class Y safety capacitor?

These safety capacitors are also known by other names, including EMI/RFI suppression capacitors and AC line filter safety capacitors. (EMI stands for electromagnetic interference and RFI stands for radio-frequency interference; RFI is simply higher-frequency EMI.) Figure 1. An example of a Class-Y capacitor. Image from this teardown.

Where are safety capacitors located in a power supply?

In isolated power supplies, safety capacitors are placed primarily in two locations: In the first case, Class X and Class y capacitors are placed in EMI filter circuits on the front end of a power supply.

Are class X and Class Y capacitors safe?

Because Class-X and Class-Y capacitors must be connected directly to AC lines (line-to-neutral or line-to-ground) in order for them to perform their EMI and RFI filtering functions, they must be rated and certified as "safety capacitors." Both Class-X and Class-Y capacitors have subclasses: subclass X1, X2, and X3, and subclass Y1, Y2, Y3, and Y4.

What is the capacitance requirement for a safety capacitor?

The capacitance requirement for this connection is that the safety capacitor’s value must be much larger than the parasitic winding capacitance. This usually means a Class Y capacitor with 1 nF to 1 uF will work, depending on the frequency range required to bypass to the primary side of the system.

Are Vishay safety capacitors UL compliant?

All safety capacitors are approved according to IEC 60384-14.4, UL, and CQC, while all series are compliant with RoHS and the REACH regulations. Vishay’s line of X1 / Y2 and X2 surface-mount safety capacitors offers devices for operating voltages up to 250 VAC. As surface-mount devices, the capacitors simplify circuit board assembly.